The long-term goal of this project is to understand the mechanisms by which children with auditory-based learning problems have difficulty learning. Previous research has established that these children have particular difficulty discriminating speech sounds differing only in their formant transitions, likely due to a more general auditory deficit in processing rapid sounds. This deficiency has been related to a weaker left-cortical dominance to rapid sounds. The proposed study will use functional magnetic resonance imaging to demonstrate lateralization patterns of temporal and spectral acoustic processing in normal children (NL) and children with auditory-based learning disabilities (LP). Two series of stimuli will be derived from a standard stimulus consisting of two pure tones separated by an octave and alternating at a slow rate. One series will systematically increase the rate of frequency modulation while keeping spectral complexity constant, and the other will increase spectral complexity while keeping a constant rate. NL children are predicted to show more activity in left auditory cortical regions with increasing rate of frequency modulation, while LP children show weaker lateralization. Increased spectral complexity is expected to elicit right-lateralized responses in both groups. Differences in structural aspects of the white matter of Heschl's Gyri (HG) will be investigated. White matter volumes and anisotropy (a measure of microstructural integrity) will be measured in right and left HG of all children and related to individual laterality indices. Larger white matter volumes have been found in left than right HG in normal brains, likely due to thicker myelination of axons which allow faster transfer of information, a necessary component of rapid signal processing. Smaller white matter volume or abnormal anisotropy in left HG could potentially be underlying deficiencies of fast auditory processing in LP children. An important aspect of the proposed study is the availability of data from a wide variety of perceptual, educational, and electrophysiologic measures related to speech perception that have already been collected from all subjects. This will allow a systematic assessment of relationships between these measures and functional laterality indices. It is expected that the integration of data across these many methodologies within individual children will reveal relationships that have previously been difficult to uncover when comparing across different groups of subjects in different studies.